Fluoroelastomers have achieved outstanding commercial success and are used in a wide variety of applications in which severe environments are encountered, in particular those end uses where exposure to high temperatures and aggressive chemicals occurs. For example, these polymers are often used in seals for aircraft engines, in oil-well drilling devices, and in sealing elements for industrial equipment that operates at high temperatures.
The outstanding properties of fluoroelastomers are largely attributable to the stability and inertness of the copolymerized fluorinated monomer units that make up the major portion of the polymer backbones in these compositions. Such monomers include vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene and perfluoro(alkyl vinyl) ethers. In order to develop elastomeric properties fully, fluoroelastomers are typically crosslinked, i.e. vulcanized. To this end, a small percentage of cure site monomer is copolymerized with the fluorinated monomer units. Cure site monomers containing at least one cyano group, for example perfluoro-8-cyano-5-methyl-3,6-dioxa-1-octene, are especially preferred. Such compositions are described in U.S. Pat. Nos. 4,281,092; 4,394,489; 5,789,489; 5,789,509 and in WO 2011084404.
U.S. Pat. No. 8,288,005 B2 discloses perfluoroelastomers having cyano cure sites that are cured with certain aliphatic mono-, di- and poly-azides. However, these azides may be difficult to synthesize and can be challenging to purify via distillation. The azides tend to have poor stability (both thermal and explosive). Also the azides are usually liquids at room temperature which can make it difficult to compound with fluoroelastomers.
U.S. Pat. No. 8,288,482 B2 discloses perfluoroelastomers having cyano cure sites that are cured with certain diazides. These diazides may suffer from many of the deficiencies mentioned above.
Fluoropolymers having pendant sulfonyl azide groups are disclosed in U.S. Pat. No. 6,365,693 B1. These fluoropolymers generally have good chemical stability, so they are relatively easy to handle.